1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a stator vane in an industrial gas turbine engine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as a large frame heavy-duty industrial gas turbine (IGT) engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine—and therefore the engine—can be increased by passing a higher temperature gas stream into the turbine. However, the turbine inlet temperature is limited to the material properties of the turbine, especially the first stage vanes and blades, and an amount of cooling capability for these first stage airfoils.
The first stage rotor blade and stator vanes are exposed to the highest gas stream temperatures, with the temperature gradually decreasing as the gas stream passes through the turbine stages. The first and second stage airfoils (blades and vanes) must be cooled by passing cooling air through internal cooling passages and discharging the cooling air through film cooling holes to provide a blanket layer of cooling air to protect the hot metal surface from the hot gas stream.
The turbine of the engine includes rows of stator vanes and rows of rotor blades with labyrinth seals formed between the stationary vanes and the rotating blades to prevent hot gas from the mainstream flow entering into the rim cavities within the inter-stage housing of the turbine. The turbine rotor disks are limited to lower temperatures than are the airfoils of the vanes and blades in order to provide for long service life. Excessive temperature exposure will result in cracks in rotor disks that can lead to shortened life or in some cases failure of the rotor disk such as exploding into pieces.
Turbine vanes are produced using an investment casting process in which a ceramic core is used to form the internal cooling air passages of the airfoil. The ceramic core must be retained in position within a mold during the liquid molten metal pouring operation in forming the vane. Core shift or core breakage results in low casting yields which directly result in high cost of the parts.